Communication network comprising at least a source and a switch for receiving and forwarding data packets originated by the source

ABSTRACT

Communication network comprising a source and a switch for receiving and forwarding data packets originating from the source, wherein the network comprises at least two mutually different routing paths between the source and the switch, wherein the switch comprises at least two incoming ports for receiving the data packets originating from the source, wherein the switch is arranged to discard for a period of time any data packet originating from the source at the first one of the at least two incoming ports upon receiving a data packet originating from the source at the second one of the at least two incoming ports after receiving a data packet originating from the source at the first one of the at least two incoming ports.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority of European Application No.02254976.0 filed on Jul. 16, 2002.

[0002] 1. Field of the Invention

[0003] The invention is related to a communication network comprising atleast a source and a switch for receiving and forwarding data packetsoriginating from the source, wherein the network comprises at least twomutually different routing paths between the source and the switch,wherein the switch comprises two incoming ports for receiving datapackets originating from the source.

[0004] 2. Background of the Invention

[0005] Such communication network is known per se.

[0006] In use, one or more sources are directly or indirectly connectedwith the switch. If a source is directly connected with a switch, directconnections, referred to as paths, are for example present between thesource and the switch. If a source is indirectly connected with theswitch at least one other switch is present between the switch and thesource. Between two switches there are often two mutually differentrouting paths. Each data packet generally comprises information withrespect to the source the data packet originates from as well asinformation related to the destination address where to the data packetis sent. Each switch of the network is capable of extracting theinformation related to the destination address enabling the switch toforward the data packet into the right direction. Each switch isgenerally also capable of extracting from the data packet the sourcefrom which the packet originates.

[0007] In practice, there usually is a difference in length of time usedfor transferring a data packet originating from the source to the switchdepending on the path used. The path followed over the network maysometimes have to be altered quickly during the transit of a number ofdata packets originating from the source. This need for a quickalteration of the path may, for instance, be a result of a link failure,a result of a desire to use a faster path, or the result of managementaction leading to the use of a different path. Such a quick change of apath may at some point in time lead to an arrival of the data packets atthe switch in an order which is different from the order in which theywere sent by the source.

[0008] For instance, let's assume that data packet X with a destinationaddress B is sent from the source A before data packet Y with adestination address B is sent from the source A and that a change ofpath occurs during the transit of packet X and packet Y. If this changeonly leads to a new path for Y and this new path for Y is faster thanthe path used by X, packet Y will at some point arrive at the switchbefore packet X has arrived at that switch. In some uses of the network,such as the use of the network as a bridged Ethernet network, thisre-ordering of the data packets during the transit causes problems withregard to the interpretation of such a re-ordered series of data packetsat the final destination address B.

[0009] It should be noted that within the context of this specificationdata packets are said to have been re-ordered and an order of datapackets is said to be different from an other order of the very samedata packets if at least one data packet which was sent before an otherdata packet is received by a switch or a destination address after theother data packet has been received by that switch.

[0010] The problem of re-ordering during transit may be solved byproviding each data packet with a sequence number to allow for orderingthe data packets back into the order according to which the data packetswere sent by the switch. This occurs in protocols such as TCP/IP.However, this leads to extra overhead in the length of a data packet andthe packet processing.

[0011] It is an object of the invention to provide a communicationnetwork with a switch which is arranged to prevent re-ordering of datapackets.

SUMMARY OF THE INVENTION

[0012] The object is achieved by a communication network according tothe invention which is characterised in that the switch is arranged todiscard for a period of time any data packet originating from the sourceat the first one of the at least two incoming ports upon receiving adata packet originating from the source at the second one of the atleast two incoming ports after receiving a data packet originating fromthe source at the first one of the at least two incoming ports. This hasthe advantage that upon receiving a data packet originating from thesource at the second one of the at least two incoming ports afterreceiving a data packet originating from the source at the first one ofthe at least two incoming ports another data packet from the source canfor a period of time not be received at the first one of the at leasttwo incoming ports. This other data packet originating from the sourcemay have been sent from the source before the data packet received atthe second one of the at least two incoming ports was sent from thesource. By discarding this other data packet, re-ordering of datapackets is prevented.

[0013] In a particular embodiment of a communication network accordingto the invention, the switch is further arranged to discard for a periodof time any data packet originating from the source at all the at leasttwo incoming ports apart from at the second one, upon receiving a datapacket originating from the source at the second one of the at least twoincoming ports after receiving a data packet originating from the sourceat the first one of the at least two incoming ports. In this case, atnone of the at least two incoming ports apart from at the second one,data packets originating from the source are received. This is ofparticular interest in cases where the switch “learns” from the port atwhich a data packet originating from the source is received, which pathshould be followed by a data packet with the destination address of thatsource. In other words, if a switch receives a given data packet with adestination address, the switch will forward that given data packet fromthe port at which it has just received another data packet from thesource with that destination address. When packets from a certain sourceaddress arrive alternatingly at two ports of the same switch, also theforwarding of data packets to this source address will alternatinglyoccur from these two ports. The negative effect is that packets arelikely to get lost. However, this particular embodiment prevents thecontinuous changing of ports from which data packets are forwarded.

[0014] In one embodiment of a communication network according to theinvention, the period of time lasts till the switch is informed thatre-ordering of the data packets originating from the source is no longerpossible. This may be due to a management action or for instance to thefact that it is known that a last data packet of a series of datapackets has arrived at its destination address. The predetermined lengthof time can be set such that it is highly likely that within the lengthof time a complete series of data packets will arrive at only one portof the switch.

[0015] Preferably the communication network according to the inventionis characterized in that, the communication network is used by anEthernet Network.

[0016] The invention is further related to a switch for use in acommunication network which further comprises a source and, when theswitch is in use, at least two mutually different routing paths betweenthe source and the switch, wherein the switch is arranged to receive andforward data packets originating from the source, wherein the switchcomprises at least two incoming ports for receiving the data packetsoriginating from the source.

[0017] The invention is further related to a switch for use in such acommunication network.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention is herebelow explained by the following, nonlimiting example as illustrated in the drawing. Herein shows:

[0019]FIG. 1 schematically a communication network according to theinvention during a first stage of use;

[0020]FIG. 2 schematically the communication network of FIG. 1 during asecond stage of use;

[0021]FIG. 3 schematically the communication network of FIG. 1 during athird stage of use;

[0022]FIG. 4 schematically the communication network of FIG. 1 during afourth stage of use;

[0023]FIG. 5 schematically the communication network of FIG. 1 during afifth stage of use;

[0024]FIG. 6 schematically the communication network of FIG. 1 during asixth stage of use;

[0025]FIG. 7 schematically the communication network of FIG. 1 during aseventh stage of use;

[0026]FIG. 8 schematically the communication network of FIG. 1 during aeighth stage of use;

[0027]FIG. 9 schematically the communication network of FIG. 1 during aninth stage of use;

[0028]FIG. 10 schematically the communication network of FIG. 1 during atenth stage of use

[0029]FIG. 11 schematically the communication network of FIG. 1 during aeleventh stage of use.

DETAILED DESCRIPTION

[0030]FIG. 1 shows a communication network N comprising switch S1 and aswitch S2. The network N comprises between the switch S1 and switch S2two paths I, II. Switch S2 comprises a port p2 for receiving packetsoriginating from source A as forwarded by switch S1 along path II and aport p1 for receiving packets forwarded by switch S1 along path I. Fromsource A the packets 1,2,3,4 are sent with destination address B. Afterforwarding data packet 1,2 from switch S1 along path I the route fromswitch S1 to switch S2 is changed from path I to path II, as shown inFIG. 2. Hence, data packets 3,4 are forwarded along path II towardsswitch S2. Path II is in this example faster than path I. FIG. 3 showsthat data packet 1 is received at port p1 of switch S2, while datapacket 2 is still travelling along path I and data packets 3,4 are stilltravelling along path II. As path II is faster than path I, data packet3 is received at port p2 of switch S2 before data packet 2 has arrivedat port p1 of switch S2. This is shown in FIG. 4.

[0031] According to the invention, in this situation data packetsarriving at port p1 are for a period of time discarded once data packetsforwarded by switch S1 are received at port p2 of switch S. FIG. 5 showsin accordance with the invention that data packet 2 is not forwarded byswitch S2 to destination B and FIG. 6 shows that data packet 2 isdiscarded by port p1 while data packet 4 is received at port p2 ofswitch S1. Within the context of this specification receiving a datapacket implies accepting the data packet and if needed forwarding thedata packet. Discarding a data packet implies not accepting the arrivalof a data packet. It follows that data packet 4 is not discarded and isforwarded by switch S2 towards destination address B, finally leading tothe arrival of data packets 1,3 and 4 at destination address B as shownin FIG. 7.

[0032] It is of course also possible that switch S2 comprises many moreports p1, p2, . . . px for receiving data packets forwarded by theparticular switch S1. In that case it is possible that instead ofdiscarding data packets for a period of time only at port p 1 uponreceiving data packets at port p2, data packets are for a period of timediscarded at all other ports p1, . . . px apart from at port p2.

[0033] It is equally possible that the source is capable of sending datapackets via two or more different paths to switch S1. Re-ordering is inthis case prevented as long as switch S1 is arranged as switch S2, i.e.according to the invention. In other words, as long as switch S1 isarranged to discard for a period of time any data packet originatingfrom the source at port p1 upon receiving a data packet originating fromthe source at port P2 after receiving a data packet originating from thesource at port p1, re-ordering is prevented.

[0034] Although the example only shows one source, it is also possiblethat a plurality of sources is capable of sending data packets to switchS1. As a switch is capable of extracting from the data packetinformation related to the source from which the data packet originates,the switch may according to the invention at one or more ports discardor accept data packets depending on the source from which the datapacket originates.

[0035] A period of time may last till switch S2 is informed thatre-ordering of the data packets originating from source A is no longerpossible. It is however also possible that the period of time has apredetermined length of time which is for instance chosen such that itis unlikely that re-ordering is still possible once the predeterminedlength of time has passed. FIG. 8 to FIG. 11 illustrate the situationafter expiration the period of time, either due to the fact that theperiod of time comprises a predetermined length of time which haspassed, or due to the fact that the switch has been informed thatre-ordering of the data packet is no longer possible. Data packets 5,6,7from source address A may for instance again be forwarded by switch S1along path I towards switch S2. These data packets are in that casereceived by port p1 and all forwarded by switch S2 towards destinationaddress B.

[0036] The communication network according to the invention isespecially suitable if used by an Ethernet network.

[0037] It is of course possible that in a communication networkaccording to the invention each switch comprises a switch which is beingarranged to discard for a period of time any data packet originatingfrom a source at port p1 upon receiving a data packet originating fromthat source at port p2 after receiving a data packet originating fromthe source at port 1. A network may comprise many switches and manypaths between the switches. It is also possible that to each switch anumber of end stations are connected. All these end stations have anaddress. Each of these variations and extensions are understood to fallwithin the framework of the invention as defined by the appended claims.

1. Communication network comprising a source and a switch for receivingand forwarding data packets originating from the source, wherein thenetwork comprises: at least two mutually different routing paths betweenthe source and the switch, wherein the switch comprises at least twoincoming ports for receiving the data packets originating from thesource, the switch operable to discard for a period of time any datapacket originating from the source at the first one of the at least twoincoming ports upon receiving a data packet originating from the sourceat the second one of the at least two incoming ports after receiving adata packet originating from the source at the first one of the at leasttwo incoming ports.
 2. Communication network according to claim 1,characterised in that, the switch is further arranged to discard for aperiod of time any data packet originating from the source at all the atleast two incoming ports apart from at the second one, upon receiving adata packet originating from the source at the second one of the atleast two incoming ports after receiving a data packet originating fromthe source at the first one of the at least two incoming ports. 3.Communication network according to claim 1, characterised in that, theperiod of time lasts till the switch is informed that re-ordering of thedata packets originating from the source is no longer possible. 4.Communication network according to claim 1, characterised in that, theperiod of time has a predetermined length of time.
 5. Communicationnetwork according to claim 1, characterised in that the communicationnetwork is used by an Ethernet Network.
 6. Switch for use in acommunication network which includes a source and, when the switch is inuse, at least two mutually different routing paths between the sourceand the switch, wherein the switch is arranged to receive and forwarddata packets originating from the source, wherein the switch comprises:at least two incoming ports for receiving the data packets originatingfrom the source, the switch operable to discard for a period of time anydata packet originating from the source at the first one of the at leasttwo incoming ports upon receiving a data packet originating from thesource at the second one of the at least two incoming ports afterreceiving a data packet originating from the source at the first one ofthe at least two incoming ports.
 7. Switch according to claim 6,characterised in that, the switch is further arranged to discard for aperiod of time any data packet originating from the source at all the atleast two incoming ports apart from at the second one, upon receiving adata packet originating from the source at the second one of the atleast two incoming ports after receiving a data packet originating fromthe source at the first one of the at least two incoming ports. 8.Switch according to claim 6, characterised in that, the period of timelasts till the switch is informed that re-ordering of the data packetsoriginating from the source is no longer possible.
 9. Switch accordingto claim 6, characterised in that, the period of time has apredetermined length of time.
 10. Switch according to claim 6,characterised in that the communication network is used by an EthernetNetwork.